Caption: Tissue culture of the tobacco plant Nicotiana tabacum growing in a petri dish on nutrient agar. The tissue cultures are grown from tobacco calluses, parenchymatous cells that form around a wounded plant surface. The mass of undifferentiated cells, or even a single cell, is placed on a sterile culture medium containing salts, a variety of organic materials, vitamins & growth substances. After a period of time shoots & leaves emerge & a normal, healthy plant is regrown. Tissue culture has various applications in plant breeding.